This invention relates generally to burner control systems and, more particularly, to fuel valve control circuits.
Extensive efforts have been directed toward improving control systems for fuel burners such as gas and oil burners and the like. Increased system safety and reliability have been primary objectives of such efforts.
Most burner systems employ fuel supply valves that are automatically controlled by start-up circuits and some type of flame detecting mechanism that automatically interrupts fuel flow in response to a predetermined loss of flame condition. Typical start-up circuits initiate fuel flow only after a delay period provided, for example, to permit purging of previously discharged fuel or activation of a fuel ignition system. The more serious problems caused by malfunctions in these circuits are either a premature opening of the valve or a retention thereof in an open position in the absence of flame. Many circuits have been developed that include numerous safeguards to insure that such unsafe conditions will not result if one or more circuit components fail. However, prior control circuits have not prevented unsafe operation in the event that the relay contacts energizing the valve solenoid are inadvertently closed. Such a situation can exist, for example, when contacts become welded closed.
An object of this invention therefore, is to provide a failsafe valve control system that will prevent unsafe conditions upon an inadvertent closure of relay contacts connected to a valve solenoid. A further object is to establish a positive lock out in response to such a condition.